1. Field of the Invention
The present invention relates to a surface emission semiconductor laser device, and more particularly, it relates to a surface emission semiconductor laser device comprising a multi-layer reflector.
2. Description of the Background Art
A surface emission semiconductor laser device of a vertical resonance type has been actively developed in recent years. This surface emission semiconductor laser device, having excellent characteristics such as a low threshold current, high-speed response, easiness in implementation of a two-dimensional array and a low cost, is expected for various applications in the fields of optical communication, optical recording and optical measurement.
In the conventional surface emission semiconductor laser device, however, it is difficult to control the plane of polarization in a prescribed direction since the cavity is concentric with respect to the traveling direction of the laser beam. Therefore, the plane of polarization may unstably switch between two planes of polarization along the <110> and <1–10> crystal orientations of an emission layer. Consequently, it is difficult to stably control the plane of polarization in the conventional surface emission semiconductor laser device. Thus, it is difficult to combine the surface emission semiconductor laser device having the difficulty in stably controlling the plane of polarization with an optical component such as a polarized beam splitter or a polarizer. In optical communication, further, switching of the plane of polarization disadvantageously hinders high-speed modulation.
Various methods have been proposed for stably controlling the plane of polarization of the surface emission semiconductor laser device. For example, Japanese Patent No. 3,123,136 discloses a method of controlling the plane of polarization of a surface emission semiconductor laser device by employing a semiconductor substrate (inclined substrate) having a plane orientation inclined in a specific direction. This method controls the plane of polarization by supplying a high optical gain to the plane of polarization of the specific direction due to anisotropy of the crystal orientation of an emission layer with respect to the direction for emitting a laser beam.
In the aforementioned method disclosed in Japanese Patent No. 3,123,136 capable of improving the optical gain with respect to polarization in a prescribed direction, however, an optical gain with respect to polarization in another direction is not zero and hence the plane of polarization is disadvantageously insufficiently controlled. Further, it is difficult to individually control the planes of polarization of surface emission semiconductor laser devices formed on the same substrate since the plane orientation of the overall substrate is inclined in the specific direction.